All that foam deteriorates. MEK and a wood toothpick clean out the old junk. Work outside.

I redid my F2, Nikormat, and FE2 with acryllic yarn in the groves and black felt for the mirror damper. I wish I could remember the adhesive or could find it. These three will never need fixing again.

Top end movie cameras all use yarn.

Anyway all three worked the first try and have remained good for a year +